(1) Prior Art for Modification of Surface Property of Polymeric Materials
Polyolefin material, such as polypropylene and polyethylene, is excellent in lightness, strength, chemical resistance, and so forth, and is widely used for molded goods, such as a film, a non-woven fabric, and automobile parts, electrical machinery and apparatus parts. However, as polyolefin materials have a low polarity and a high crystallinity, which are derived from its chemical structure, they have a small hydrophilic property and a difficulty in chemical modification. Therefore, they have a low hydrophilic property and a difficulty in the chemical modification. Various surface activation processings such as ozonization, plasma treatment, UV irradiation processing, high-pressure electro-discharge treatment, corona discharge processing, sandblasting processing, solvent etching processing, chromium mixed-acid processing, and a flame treatment, and so forth have been tried in order to improve the hydrophilic property and an adhesive property of the polyolefin material. However, even if any method of the above processes is employed to treat the polyolefin material, we cannot obtain the material which absorbs water as much as several times of the original weight of the material.
For example, the method of improving plating nature, paint nature, and an adhesive property was examined by performing an ozone oxidation treatment (JP, 3-103448,A (1991)). However, when only the ozone treatment is employed to improve the property of the material, very severe reaction conditions are necessary and they cause the decrease in the mechanical strength, which makes that the treatment is non-practical. Furthermore, it is impossible to give a large water absorption property to the material only by the ozone treatment. In order to modify the materials by the other treatments mentioned above, the following problems are caused; the lowering in mechanical strength of the material and the high cost for facilities and a waste disposal system.
In addition to the direct activation of the surface of polymeric materials mentioned above, a method to form a layer which consists of a component with high reactivity on the surface of polymeric materials was proposed. For example, it was proposed that vinyl monomers containing ester groups were grafted to the nonwoven fabric of polyolefin fiber and then, the ester groups were hydrolyzed to form acid groups which gave a hydrophilic property and an ion-exchange property (JP, 11-7937,A (1999)). However, a grafting of sufficient amount which gives a high hydrophilic property to polyolefins is not easily attained by the vinyl monomer grafting according to the proposed method. Moreover, the method requires the hydrolysis treatment after the grafting, which causes a problem of taking time and effort.
On the other hand, a method to improve a hydrophilic property of nonwoven fabrics of polyolefin fiber by the treatment with a hydrophilic resin in the presence of a persulfate was proposed (JP,11-67183,A (1999)). Although this method gave practically a hydrophilic property to the nonwoven fabrics, the modified hydrophilic property does not give a durability in use. For instance, the hydrophilic property obtained by this method is lost considerably by washing with a hot detergent solution. In addition, when the materials such as films and casts other than a nonwoven fabric were processed, sufficient hydrophilic property could not be given, or the adhesive property by adhesives could not be improved. A method to modify a hydrophilic property of nonwoven fabrics by coating polyvinyl alcohol (JP,1-248460,A (1989)) was also known. Although the hydrophilic property of the obtained material is high, it has the problem that the durability of a hydrophilic property is not enough because the process is mere covering.
Previously, the present applicant proposed a method to improve the surface property or especially the dyeability of polymeric materials, which comprises an activation treatment of the surface of polymeric materials, a graft polymerization of monomers such as acryl amide, etc. to them or the Hofmann rearrangement of the amide groups which are contained in grafts (JP,8-109228,A (1997)). Although the polymeric materials which gave the hydrophilic property on the basis of this method can be manufactured by this method, the kind of polymeric materials which can be applied by the method is limited.
According to these methods, polymeric materials with a high water absorption property can be manufactured cheaply and easily. However, when the moldings of the polymeric materials containing additives such as a stabilizer and an antioxidant are processed to obtain a high durable hydrophilic property, these additives may reduce the effect of the activation process.
The above technical requests are desirable not only for polyolefins but also the other polymeric materials which have more active surface property than polyolefins. For example, it is sometimes requested that a surface of a polymeric material is modified to give a desirable property.
(2) Prior Art for Dentition Orthodontic Appliances
A dentition orthodontic appliance is used to correct an irregular alignment of teeth by a restitution force which is caused by an elastic steel wire (so-called arch wire) penetrating through an appliance (so-called bracket) that is bonded to a tooth. In general, a bracket is made of metal or ceramic. But, brackets made of polymers were produced recently.
In the brackets made of polymeric materials, a bracket made of polycarbonate resin reinforced by glass fiber (a PC bracket) is a typical one, and it was disclosed in a Japanese Patent (JP, No. 9-98988,A) and an U.S. Pat. No. 5254992. However, the PC bracket gives a low durability in the adhesive property to teeth and is easily polluted when it is used by fitting to teeth. In addition, it was reported that the PC bracket produces bisphenol A which is considered to give an environmental pollution. Because of these problems, it is desirable to invent a bracket made of a polymer resin which is harmless to a living body, is not polluted easily, and gives a strong adhesion force to teeth. As the present invention can improve the adhesive property of polyolefins which are known to be chemically stable, this technique should be also applied to nylon and polyester, and so forth. Therefore, the present invention can provide the dentition orthodontic appliances which are made of ideal polymeric materials. Moreover, the dentition orthodontic appliances mean not only brackets but also various appliances which are useful for a dental treatment.
(3) Prior Art for Members in Writing Implements or Painting Tools for Stationary or Makeup.
Various members such as ink-collectors (or ink-regulators), ink-tanks, ink-guiding cores, pen cores, center rods for pens, ink-absorbing materials made of fibers, ink-retaining sponges, brush heads of brush pens, and so forth are used in writing implements. Almost of these members are generally made of polymeric materials. Because, the polymeric material gives a high mechanical strength, an easy casting property, a chemical resistance, economics, and so forth. Members in writing imprements which are used to contact to water-soluble ink require a wettability to water-soluble ink, an absorptivity of the ink and an ink-retaining property. In order to overcome these requirements, a development in excellent and safety skills to improve the hydrophilic property of synthetic polymers has been expected.
One of the typical members of writing implements is an ink collector (which is sometimes called “a collector” in short below). The collector is explained in detail here. The collector is used in an ink tank of a writing implement where the ink is stored directly and it plays an ink retaining body. When an expansion of the air in an ink tank is caused by a temperature increase or a lowering of the atmosphere pressure, the ink pressured in the ink tank run through several longitudinal channels on the collector surface and then it is stored in many horizontal channels (which are called as ink-retaining channels) which are perpendicular to the longitudinal channel. Thus, the outflow of the pressured ink from air voids and nibs of pens can be avoided. When the temperature or the air pressure are recovered to the original state, it is necessary that the ink stored in the ink-retaining channels comes back to the ink tank through the longitudinal channels. When a writing implement is used for a long time, a decrease in air pressure in the ink tank is caused by a decrease in the amount of ink. As a result, when the decrease in air pressure is caused to excess, the amount of ink suitable for a good writing cannot be drawn from the nib of pens. In order to avoid this problem, the pressure in the ink tank must be kept at a given reduced pressure. Therefore, the ink collector has a mechanism that the wasted ink is substituted with the corresponding volume of air by the longitudinal channels in the ink tank. When a writing implement is equipped with an ink tank with an excellent collector whose structure is preferable for storing ink directly, we can use it with a constant amount of ink from the first writing to the final writing.
In addition, a writing implement with a collector made of synthetic resin has the following advantages. It gives a good consumption of ink as compared with the collector containing an ink absorber made of fibers; we can use the ink stored in the collector almost completely without leaving it in the ink tank. We can see the amount of ink easily through an ink tank which is made of a transparent polymer resin.
Therefore, a collector is an indispensable member for a writing implement with an ink tank. However, when an ink collector surface has an insufficient wettability to ink, the ink pressured in the ink tank cannot run smoothly into the ink-retaining channels of the collector and the retention power of the collector to the ink is too weak to keep the ink in the collector, without a capillary attraction. As a result, the ink contained in the collector goes out of the ink-retaining channels easily and the ink outflows from the air voids.
At present, an ABS resin (a three-components copolymer of acrylonitrile, butadiene and styrene) is generally used as a material for the collector, because of the strength, the casting property, the reason that the improvement of the wettability is comparatively easy, and so forth. Collectors cast by the ABS resin are treated by immersing them in strong acids or strong alkalis for several minutes to form hydrophilic groups on them in order to improve their wettability. For example, chromic mixed acid or sodium hydroxide are used as an acid or an alkali. However, the treatment has the following problems; a dangerous working and the difficulty in the treatment of waste liquid. In addition, when the washing of the collector after the treatment is not carried out completely, the following problems are considered to be caused; the waste liquid of the chemicals in the writing implement changes the quality of ink and causes a definite default in the writing implement. Although the danger in the job is high, the wettability of the ink collector to ink decreases with the elapse of time and therefore, the treatment is not satisfied well.
On the other hand, a plasma treatment was carried out to improve the hydrophilic property of ABS resin-made correctors (JP, 05-238186,A (1993)). Furthermore, a method to make a surface treatment with vinyl monomers after the plasma treatment was disclosed (JP, 05-238187,A (1993)). The plasma treatment is suitable for the surface treatment of materials with smooth surface, but it causes a defect in the treatment of correctors having concavo-convex surface because it cannot give a good result to treat the concave part of correctors.
This problem is similarly seen in the treatment of pen cores made by fiber bundles and porous materials with an ink absorptivity. Namely, it is very difficult to treat the inner part of fiber bundles and porous materials by a plasma treatment.
In addition, as the surface treatment of ABS resins is comparatively easy, an application of many general methods such as a grafting of hydrophilic monomers, an ionization radiation, a grafting by UV irradiation, and so forth is possible. However, as each of these methods has laborious processes and gives some problems in grafting such as a surface irregularity and a difficulty to obtain a controlled amount of graft polymers, it's application is not suitable for the treatment of materials such as correctors which need a precise structure.
When collectors and the other members in writing implements are cast with polyolefins such as polyethylene and poplypropylene, it is expected to give a collector with an excellent chemical resistance, a lightweight and a high-impact property and the other members of writing implement. In addition, the application of these products does not cause the environmental pollution and the toxicity of components in combustion gas which are problematic in recent years. However, it is very difficult to improve polyolefin resins by the well-known technique for hydrophilic improvement so far. Especially, as cast products of polyolefin resins should contain many kinds of additives such as stabilizers for polymer resins, chemical destaticizers, and so forth, their treatment to improve the hydrophilic property is impossible as far as the products are used as they are. Therefore, there is not an excellent method to give the improvement expected in the hydrophilic property of collectors and the other members in writing implements as described above. If the technique to improve the hydrophilic property of polyolefins including chemical stabilizers is established, its technique should be applicable for the other materials such as nylon, polyester, wool fiber, cellulose acetate, esters of polyacrylic acids, polyurethane, and so forth because the chemical treatment of these materials are easier than that of polyolefins. Therefore, the establishment of the technique for the surface modification is expected.
(4) Prior Art for Battery Separators:
Battery Separators are used to provide a smooth electromotive reaction in batteries by holding the amount of the electrolytic solution, while separating the positive electrode and negative electrode of a chemical cell and preventing a short circuit from the former. Various requirements are dependent on the kind of batteries and a lot of inventions were carried out.
For example, as the electrolytic solution of an alkaline cell is strongly alkaline, a battery separator must be an alkali-proof material. A battery separator made of polyamide non-woven fabrics used from the past has a fault that it elutes nitrogen oxides from the fiber and contracting the life of a cell by repeat use. Therefore, battery separators made of fabrics of polyolefin fibers (a bicomponent fiber is also included) such as polypropylene and polyethylene which were excellent chemical-resistant have been investigated. However, battery separators made of polyolefin materials with an excellent durable water absorption property are not seen at present.
When polyolefin fabrics with the improved water absorption property are used as battery separators, they are immersed in an aqueous sulfuric acid solution of 40 w/w % concentration in lead storage batteries, or in an aqueous solution of sodium hydroxide of 30 w/w % concentration in alkali batteries. As the charge-discharge process must be repeated in the batteries for use, the battery separators must give an excellent durability in the use for a long time as much as possible. For that purpose, a development of the method to produce hydrophilic polymeric materials excellent in chemical resistance, oxidation resistance, and so forth is desired. Further, the method which makes it possible to produce the hydrophilic polymeric material, easily, cheaply and in large quantities is desired in industry.
Although various techniques mentioned in the above “(1) Prior Art for Modification of Surface Property of Polymeric Materials” have been applied for the modification of materials for battery separators and some methods have been proposed, the materials satisfying the requirements for battery separators are not obtained.
The present invention intends to overcome the defaults in the previous methods described above and to provide a method for improving the surface property of polymeric materials which has an excellent durability without lowering the practical strength. Furthermore, the present invention intends to provide materials with water-absorption property modified for medical, sanitary, or cosmetic supplies such as disposable diapers, sanitary protection supplies, bandages, gauze, plasters with disinfectants and materials for cleaning and face cleanser pack, and so forth, brackets for dentition orthodontics, water retention materials useful for agriculture or greening in dry districts, materials for microorganism culture media, synthetic paper, filter media, medical implements (artificial organs, artificial joints, materials molded in tubes, strings and plates, and so forth) and polymeric materials with improved adhesive property and composites containing the said improved polymeric materials.
In addition, the aim of the present invention is applicable in common for all kinds of synthetic resins, regenerated fibers and natural fibers. Especially, the present invention gives a useful technique to improve polyolefins whose chemical modification is known to be difficult, and provides improved members of writing implements made of polyolefins which give the durability in the properties such as a wettability to water-soluble ink, an ink-adsorptivity and an ink-holding property.
Furthermore, the present invention intends to provide battery separators made of modified polymeric materials which give an excellent property in keeping electrolytic solutions in batteries, an alkali-resistance, an acid-resistance, a lightweight and a high mechanical strength, and intends to prepare the battery separator with the following properties cheaply and easily; that the hydrophilic treatment of the modified polymeric materials is made by real chemical bonds and that the performance data of the battery are not changed in the use for a long time, and to prepare the batteries containing these battery separators.